The Fall and Rise in Brightness of Betelgeuse

ATel #13512; Edward Guinan, Richard Wasatonic (Villanova University),Thomas Calderwood (AAVSO) and Donald Carona (Texas A& M University)
on 22 Feb 2020; 12:59 UT
Credential Certification: Edward Guinan (edward.guinan@villanova.edu)

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As previously reported (see ATel #13365, #13410 and #13439), the red supergiant Betelgeuse has been undergoing an unprecedented decrease in its visual (V) brightness since October 2019. Photometry secured over the last ~2 weeks shows that Betelgeuse has stopped its large decline of delta-V of ~1.0 mag relative to September 2019. The star reached a mean light minimum of = 1.614 +/- 0.008 mag during 07-13 February 2020. This is approximately 424+/-4 days after the last (shallower: V ~ +0.9 mag) light minimum was observed in mid-December 2018. Thus the present fading episode is consistent with the continuation of the persistent 420-430 day period present in prior photometry. Three recent observations made at Wasatonic Observatory, carried out on 18.15 UT, 20.1 and 22.07 UT February 2020, returned V = +1.585 mag , +1.574 mag, and +1.522 mag, respectively. Photometry carried out by D. Carona on 18.2 UT February 2020 returned V = +1.589 mag. In addition, Wing TiO band and near-IR measures (and corresponding temperatures and luminosities) also reached minimum values during mid-February 2020. Photometry carried out by D. Carona (Texas A&M Univ.) on 18.2 UT February 2020 returned V = +1.589 mag. Also T. Calderwood's recent observations given on the AAVSO website (https://www.aavso.org/lcg) are: V = +1.589 mag, +1.567 mag and 1.556 mag, respectively on ~17.2, 19.2, 20.2 UT February 2020. Based on these and additional observations, Betelgeuse has definitely stopped dimming and has started to slowly brighten. Thus this "fainting" episode is over but additional photometry is needed to define the brightening phase. An ESO VLT/SPHERE IR image of Betelgeuse was secured during late 2019 December by M. Montarges et al. (2020: paper in preparation). The stunning VLT/SPHERE image shows that most of lower half of star has significantly dimmed, thus providing a spatially resolved image of the star informing about the observed dimming. (https://www.eso.org/public/news/eso2003/). At the time of the VLT/SPHERE observations, Betelgeuse's brightness was V ~ +1.3 mag. As mentioned above, the star subsequently dimmed to ~1.6 mag during mid-February 2020. Observations of all kinds continue to be needed to understand the nature of this unprecedented dimming episode and what this surprising star will do next.